JP3819457B2 - Biological denitrification of wastewater - Google Patents
Biological denitrification of wastewater Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は排水の生物学的脱窒法及びその装置に関し、詳しくは、元素硫黄を還元剤として使用し、嫌気条件下に排水を生物学的に脱窒し、脱窒された排水と、活性汚泥及び元素硫黄とを膜で分離する排水の生物学的脱窒法及び嫌気槽内に固液を分離する膜分離装置を設けた生物学的脱窒装置に関する。
【０００２】
近年、内湾、内海や湖沼等の水域における窒素及び燐による富栄養化現象の進行は、水質汚濁の主要原因として大きな社会問題と化している。
これらの水質汚染の原因となる一般家庭及び工場排水に対して、特に、排水中の窒素及び燐に対して厳しい規制が実施され、又、そのための排水処理法も種々提案されている。
【０００３】
排水処理方法として最も一般的な方法は、活性汚泥による生物学的処理法であり、生物学的処理法による窒素の除去は、好気条件下でＢＯＤ酸化菌と硝化菌を用いて排水中の有機態窒素を亜硝酸又は硝酸まで酸化する工程（硝化工程）と、嫌気条件下で脱窒化菌を用い、硝化工程で生成した亜硝酸又は硝酸を窒素ガスに還元する脱窒工程の２工程により行われる。
脱窒工程では脱窒反応の還元剤としてメタノール等の水素供与体を使用しているが、脱窒反応を完全に行う為にはメタノールを過剰に使用する必要がある。この過剰のメタノールは、脱窒反応完了後は、処理排水中にＢＯＤとして残存しており、この残存メタノールを処理するために更に活性汚泥による好気処理が必要であり、その為の再曝気槽の設置と活性汚泥を分離する為の沈澱池等の固液分離のための設備が必要となる。
【０００４】
【発明が解決しようとする課題】
従来のメタノールを還元剤として使用する生物学的脱窒法は、上記のようにメタノール等の薬剤費、設備費や運転コストが高くつき、この方法の普及の妨げとなっている。
従って、本発明の目的は、還元剤としてメタノールを使用せずに、嫌気条件下に、硝酸態窒素を生物学的に脱窒処理する方法及びコンパクト化が可能な脱窒処理装置を提供することである。
【０００５】
【課題を解決するための手段】
本発明の目的は以下の発明によって達せられる。即ち、本発明は、排水中の硝酸態窒素を嫌気条件下に生物学的に脱窒処理するに際し、還元剤として粉末状あるいは粒状の元素硫黄を硝酸態窒素の２．５倍量以上使用し、処理系の温度を１０〜４０℃の範囲から選ばれる温度に保ちながら脱窒処理し、処理された排水を嫌気槽内に設けられている膜分離装置で固液分離して、少なくとも元素硫黄及び活性汚泥を嫌気槽内に留まらせ、処理水を分離排出することを特徴とする排水の生物学的脱窒法である。
【０００６】
【発明の実施形態】
次に好ましい実施形態を挙げて本発明を更に詳細に説明する。
排水中の硝酸態窒素を、還元剤として硫黄を用いた嫌気条件下の生物学的脱窒処理と分離膜による固液分離を組み合わせて処理することにより、狭いスペースで効率よく、且つ、経済的に脱窒処理をすることができる。
【０００７】
本発明で処理する硝酸態窒素を含む排水は、有機態窒素を含む排水を好気条件下に生物学的に硝化処理して亜硝酸や硝酸を含む排水や、硝化処理を経ずに最初から硝酸態窒素を含む排水である。
本発明の生物学的脱窒処理は、硝酸態窒素を含む排水の硝化工程及び脱窒工程の２工程からなる従来の生物学的脱窒処理法における脱窒工程にそのまま使用でき、還元剤としてメタノール等の溶解性有機物による水素供与体に代えて元素硫黄を使用すること以外は、生物学的脱窒処理法自体は特に限定されない。
【０００８】
還元剤としての元素硫黄（以下では、硫黄と称する。）は、水に不溶の単体の硫黄（Ｓ0 ）であり、粉末状あるいは粒状で使用される。
硫黄は少なくとも硝酸態窒素に対する理論量（硝酸態窒素の２．５倍量）以上の量を使用することが好ましい。硫黄の添加法は特に制限されず、脱窒処理を行う嫌気槽に直接、粉末状あるいは粒状のままで、もしくはこれらの水懸濁液として添加してもよいし、被処理排水に添加してもよい。又、粒状硫黄は、嫌気槽の底部に敷き詰めることもできる。
【０００９】
硝酸態窒素を含む排水は、嫌気条件下で、撹拌下に活性汚泥と接触させられて脱窒処理される。通常、処理系（嫌気槽）中の温度は１０〜４０℃であり、ｐＨは６〜９．５の範囲である。
【００１０】
脱窒処理された排水は、膜分離装置によって、処理系中の硫黄及び活性汚泥等の固形分と処理済水とに分離される。
膜分離装置は、嫌気槽内あるいは嫌気槽の外部に設けることができるが、膜分離装置は嫌気槽内に設置することが好ましい。膜分離装置を嫌気槽内に設置することにより、設備全体をコンパクトにすることができ、又、汚泥は嫌気槽に留まり、返送する必要もなく、汚泥返送の為の付帯設備を設置する必要がなく、経済的効果も大きい。
膜分離装置を使用する他の効果としては、硫黄は分離されて嫌気槽に残り、脱窒処理された処理済水中には含まれないので、残存ＢＯＤを処理する為の再曝気槽を設置する必要もなく、又、活性汚泥を分離する設備も不要となり、狭いスペースで、コンパクトな装置で効率的、且つ経済的に排水の脱窒処理が可能となる。
【００１１】
本発明で使用する膜分離装置としては、分離膜として限外濾過膜（ＵＦ膜）、逆浸透膜（ＲＯ膜）や精密濾過膜（ＭＦ膜）等を用いた分離装置が用いられる。膜の形状は、平板型、管状型、スパイラル状型及び中空繊維型のいずれでもよいが、平板型あるいは中空繊維型の浸漬型の膜が好ましく、分離膜はＵＦ膜が好ましい。
膜の材料は、被処理排水に対し耐久性を有する材質であればいずれでもよく、特に制限されない。又、膜は、硫黄と活性汚泥等の固形分と水を分離することができる孔径（ポアサイズ）を有する膜であればよい。
【００１２】
本発明の脱窒処理法のフローを、一例として実施例で使用する図１に示す装置の概略図に基づいて説明する。
原水タンクから被処理水をポンプＰにより所定の流量で嫌気槽に供給する。嫌気槽には活性汚泥が所定量添加されている。還元剤として粉末硫黄を直接嫌気槽に所定量添加し、攪拌下に被処理水の脱窒処理を行う。ｐＨコントローラーで嫌気槽内の被処理水のｐＨを水酸化ナトリウムで７．５に調整し、水温が２５℃となるように恒温装置で水温をコントロールする。活性汚泥中の硫黄脱窒菌は、硝酸態窒素中の分子状の酸素を用いて硫黄を酸化する際に発生するエネルギーによって生育するが、自栄養微生物であるので、重炭酸塩等の無機炭素源が細胞合成の為に添加される。
脱窒処理された被処理水は、嫌気槽内に設置した膜分離装置で硫黄と活性汚泥とから分離され、処理済水として放流される。
【００１３】
【実施例】
次に実施例を挙げて本発明を具体的に説明する。
実施例１
硝酸態窒素を含む排水として表１に示す組成の人工原水を用い、図１に示す装置で脱窒処理を行った。
嫌気槽の容量は１０リットルであり、該槽内の水温が処理期間中２５℃となるように該槽外壁に設けた恒温水循環槽内に恒温装置によって恒温水を循環させた。
嫌気槽には、種汚泥として硫黄脱窒菌を含む下水処理場の活性汚泥を上記の原水で１カ月間馴養させた汚泥をＭＬＳＳが８，０００ｍｇ／ｌとなるように添加した。原水は原水タンクからポンプＰにより１２．５ｍｌ／ｍｉｎの流量で嫌気槽に供給し、処理期間中原水のｐＨをｐＨコントローラーによって７．５に制御した。
還元剤である硫黄は、粉末状（１００メッシュ）で用い、直接、嫌気槽に７０ｇ（硝酸態窒素の２．７倍量）（理論量は２．５倍量）添加した。尚、硫黄は連続運転中１週間毎に７０ｇ添加した。
【００１４】
嫌気槽内には、ポアサイズが０．０３μｍの中空繊維型の膜を設置し、脱窒処理された処理水が１２．５ｍｌ／ｍｉｎのレートで分離排出されるように嫌気槽を脱窒処理によって発生した窒素ガスで加圧した。加圧のみで所定の処理水量が得られない場合には、チューブポンプにより強制的に嫌気層から中空繊維型膜を通して減圧処理により引き抜きを行った。以上の条件で４０日間の連続処理を行った。処理水中の硝酸態窒素（ＮＯ3−Ｎ）濃度（ｍｇ／ｌ）及びＣＯＤ（ｍｇ／ｌ）を測定した（本来はＢＯＤを測定すべきであるが、測定の容易さからＣＯＤを測定した。以下の例においても同様である。）。その結果を図３に示す。
図３から明らかなように、運転開始１日目より硝酸態窒素はほぼ完全に処理され、連続処理期間中を通して良好な処理を行うことができた。これは、分離された汚泥が嫌気槽内に留まり、比較例１における汚泥返送と同じ効果が得られた為である。 又、処理水中のＣＯＤは、膜分離により硫黄が除去されたため、低濃度に保たれた。
従って、本発明方法を実施することにより再曝気槽の設置は不要である。
【００１５】
【表１】
比較例１
図２に示す従来から脱窒工程で使用されている装置を用い、還元剤としてメタノールを硝酸態窒素量の３倍の量（理論量は２．４７倍量）を添加した表２に示す人工原水を脱窒処理した。他の条件は実施例１と同じ条件で４０日間の連続処理を行った。脱窒処理された処理水は、活性汚泥と処理済水とに分離する為に沈澱槽に送り、沈殿した活性汚泥はポンプＰにより嫌気槽に連続して循環した。沈澱槽を出た処理水の硝酸態窒素（ＮＯ3−Ｎ）濃度（ｍｇ／ｌ）及びＣＯＤ（ｍｇ／ｌ）を測定した。その結果を図３に示す。
図３から明らかなように、運転開始１日目より硝酸態窒素はほぼ完全に処理され、実施例１と同様に連続処理期間中を通して良好な処理を行うことができた。しかしながら、処理水中には残留メタノール由来のＣＯＤが残留しており、これを処理するために再曝気槽等の設置が必要である。
【００１７】
【表２】
【発明の効果】
以上の本発明によれば、排水中の硝酸態窒素をほぼ完全に除去することができ、さらに脱窒処理された排水中の残留ＢＯＤは低濃度であり、活性汚泥による好気処理（再曝気槽の設置）や、活性汚泥の分離及び返送の為の設備は不要である。
又、膜分離装置を嫌気槽内に設置することにより、分離された汚泥は嫌気槽に留まり、汚泥を返送する為の設備も不要である。
従って、本発明を実施することにより、狭いスペースで効率的に、且つ経済的に硝酸態窒素含有排水の脱窒処理を実施することができる。
【図面の簡単な説明】
【図１】 実施例１で使用する装置の概略図である。
【図２】 比較例１で使用する従来装置の概略図である。
【図３】 実施例１及び比較例１の処理結果を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological denitrification method for wastewater and an apparatus therefor, and more particularly, using elemental sulfur as a reducing agent, biologically denitrifying wastewater under anaerobic conditions, denitrified wastewater, and activated sludge Further, the present invention relates to a biological denitrification method for wastewater that separates elemental sulfur from a membrane and a biological denitrification device provided with a membrane separation device for separating solid and liquid in an anaerobic tank.
[0002]
In recent years, the progress of eutrophication by nitrogen and phosphorus in water areas such as inner bays, inland seas and lakes has become a major social problem as a major cause of water pollution.
Strict regulations have been implemented on general household and factory effluents that cause these water pollution, especially nitrogen and phosphorus in the effluents, and various wastewater treatment methods have been proposed.
[0003]
The most common wastewater treatment method is a biological treatment method using activated sludge. Nitrogen removal by a biological treatment method is performed using BOD oxidizing bacteria and nitrifying bacteria under aerobic conditions. There are two steps: a process that oxidizes organic nitrogen to nitrous acid or nitric acid (nitrification process) and a denitrification process that uses denitrifying bacteria under anaerobic conditions and reduces nitrous acid or nitric acid produced in the nitrification process to nitrogen gas. Done.
In the denitrification step, a hydrogen donor such as methanol is used as a reducing agent for the denitrification reaction, but in order to complete the denitrification reaction, it is necessary to use excess methanol. This excess methanol remains as BOD in the treated wastewater after the completion of the denitrification reaction, and further aerobic treatment with activated sludge is necessary to treat this residual methanol. And a solid-liquid separation facility such as a sedimentation basin for separating activated sludge.
[0004]
[Problems to be solved by the invention]
The conventional biological denitrification method using methanol as a reducing agent increases the cost of chemicals such as methanol, equipment costs, and operation costs as described above, and hinders the spread of this method.
Accordingly, an object of the present invention is to provide a method for biologically denitrifying nitrate nitrogen under anaerobic conditions without using methanol as a reducing agent, and a denitrification apparatus capable of being made compact. It is.
[0005]
[Means for Solving the Problems]
The object of the present invention can be achieved by the following invention. That is, in the present invention, when nitrate nitrogen in waste water is biologically denitrified under anaerobic conditions, powdery or granular elemental sulfur is used as a reducing agent at least 2.5 times the amount of nitrate nitrogen. The denitrification treatment is carried out while maintaining the temperature of the treatment system at a temperature selected from the range of 10 to 40 ° C., and the treated wastewater is solid-liquid separated by a membrane separation device provided in the anaerobic tank, and at least elemental sulfur and activated sludge allowed to remain in the anaerobic tank, a biological denitrification method wastewater and separating discharge the treated water.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in more detail with reference to preferred embodiments.
Efficient and economical in a narrow space by treating nitrate nitrogen in wastewater by combining biological denitrification treatment under anaerobic conditions using sulfur as a reducing agent and solid-liquid separation with a separation membrane Can be denitrified.
[0007]
Wastewater containing nitrate nitrogen to be treated in the present invention is a wastewater containing organic nitrogen that is biologically nitrified under aerobic conditions and containing nitrous acid or nitric acid, or from the beginning without nitrification treatment. Wastewater containing nitrate nitrogen.
The biological denitrification treatment of the present invention can be used as it is in the denitrification step in the conventional biological denitrification treatment method comprising two steps of nitrification of waste water containing nitrate nitrogen and the denitrification step. The biological denitrification process itself is not particularly limited except that elemental sulfur is used in place of a hydrogen donor based on a soluble organic substance such as methanol.
[0008]
Elemental sulfur (hereinafter referred to as sulfur) as a reducing agent is single sulfur (S 0 ) that is insoluble in water, and is used in the form of powder or granules.
Sulfur is preferably used in an amount of at least the theoretical amount (2.5 times the amount of nitrate nitrogen) relative to nitrate nitrogen. The method for adding sulfur is not particularly limited, and it may be added directly to the anaerobic tank for denitrification treatment in the form of powder or granules, or as a water suspension of these, or added to the wastewater to be treated. Also good. Granular sulfur can also be spread on the bottom of an anaerobic tank.
[0009]
Wastewater containing nitrate nitrogen is subjected to denitrification treatment under contact with activated sludge under anaerobic conditions. Usually, the temperature in a processing system (anaerobic tank) is 10-40 degreeC, and pH is the range of 6-9.5.
[0010]
The denitrified waste water is separated into solids such as sulfur and activated sludge in the treatment system and treated water by a membrane separator.
The membrane separator can be provided in the anaerobic tank or outside the anaerobic tank, but the membrane separator is preferably installed in the anaerobic tank. By installing the membrane separation device in the anaerobic tank, the entire facility can be made compact, and the sludge stays in the anaerobic tank and there is no need to return it, and it is necessary to install ancillary equipment for returning the sludge. There is also a great economic effect.
Another effect of using the membrane separation apparatus is that sulfur is separated and remains in the anaerobic tank, and is not included in the treated water that has been denitrified, so a re-aeration tank is installed to treat the remaining BOD. There is no need, and no facility for separating activated sludge is required, and it is possible to efficiently and economically denitrify wastewater in a small space and with a compact apparatus.
[0011]
As the membrane separation device used in the present invention, a separation device using an ultrafiltration membrane (UF membrane), a reverse osmosis membrane (RO membrane), a microfiltration membrane (MF membrane) or the like is used as a separation membrane. The shape of the membrane may be any of a flat plate type, a tubular type, a spiral type, and a hollow fiber type, but a flat plate type or a hollow fiber type immersion type membrane is preferable, and a separation membrane is preferably a UF membrane.
The material of the membrane may be any material as long as it is durable to the wastewater to be treated, and is not particularly limited. Further, the membrane may be a membrane having a pore size (pore size) capable of separating solids such as sulfur and activated sludge and water.
[0012]
The flow of the denitrification method of the present invention will be described based on the schematic diagram of the apparatus shown in FIG. 1 used in the embodiment as an example.
Water to be treated is supplied from the raw water tank to the anaerobic tank at a predetermined flow rate by the pump P. A predetermined amount of activated sludge is added to the anaerobic tank. A predetermined amount of powder sulfur is directly added to the anaerobic tank as a reducing agent, and denitrification treatment of the water to be treated is performed with stirring. The pH of the water to be treated in the anaerobic tank is adjusted to 7.5 with sodium hydroxide with a pH controller, and the water temperature is controlled with a thermostatic device so that the water temperature becomes 25 ° C. Sulfur denitrifying bacteria in activated sludge grows with the energy generated when sulfur is oxidized using molecular oxygen in nitrate nitrogen, but since it is a self-feeding microorganism, it is an inorganic carbon source such as bicarbonate. Is added for cell synthesis.
The denitrified water to be treated is separated from sulfur and activated sludge by a membrane separator installed in an anaerobic tank and discharged as treated water.
[0013]
【Example】
Next, an Example is given and this invention is demonstrated concretely.
Example 1
The artificial raw water having the composition shown in Table 1 was used as the waste water containing nitrate nitrogen, and the denitrification treatment was performed using the apparatus shown in FIG.
The capacity of the anaerobic tank was 10 liters, and constant temperature water was circulated by a constant temperature apparatus in a constant temperature water circulation tank provided on the outer wall of the tank so that the water temperature in the tank was 25 ° C. during the treatment period.
To the anaerobic tank, sludge obtained by acclimatizing activated sludge from a sewage treatment plant containing sulfur denitrifying bacteria as seed sludge for 1 month with the above raw water was added so that the MLSS would be 8,000 mg / l. The raw water was supplied from the raw water tank to the anaerobic tank at a flow rate of 12.5 ml / min by the pump P, and the pH of the raw water was controlled to 7.5 by the pH controller during the treatment period.
Sulfur, which is a reducing agent, was used in powder form (100 mesh), and was directly added to an anaerobic tank in an amount of 70 g (2.7 times the amount of nitrate nitrogen) (theoretical amount was 2.5 times the amount). In addition, 70g of sulfur was added every week during continuous operation.
[0014]
A hollow fiber membrane with a pore size of 0.03 μm is installed in the anaerobic tank, and the anaerobic tank is denitrified so that the treated water that has been denitrified is separated and discharged at a rate of 12.5 ml / min. Pressurized with the generated nitrogen gas. When a predetermined amount of treated water could not be obtained only by pressurization, the tube pump was forcibly pulled out from the anaerobic layer through a hollow fiber type membrane by decompression. Under the above conditions, continuous treatment for 40 days was performed. Although treated water nitrate nitrogen (NO 3 -N) concentration (mg / l) and COD of (mg / l) was measured (originally should be measured BOD, it was measured COD ease of measurement. The same applies to the following examples.) The result is shown in FIG.
As is apparent from FIG. 3, nitrate nitrogen was almost completely treated from the first day of operation, and good treatment could be performed throughout the continuous treatment period. This is because the separated sludge stayed in the anaerobic tank and the same effect as the sludge return in Comparative Example 1 was obtained. In addition, COD in the treated water was kept at a low concentration because sulfur was removed by membrane separation.
Therefore, it is not necessary to install a re-aeration tank by carrying out the method of the present invention.
[0015]
[Table 1]
Comparative Example 1
Table 2 shows an artificial device shown in Table 2 in which methanol used as a reducing agent is added three times the amount of nitrate nitrogen (theoretical amount is 2.47 times the amount) using the apparatus conventionally used in the denitrification step shown in FIG. Raw water was denitrified. The other conditions were the same as in Example 1, and the continuous treatment was performed for 40 days. The treated water subjected to denitrification treatment was sent to a sedimentation tank for separation into activated sludge and treated water, and the precipitated activated sludge was circulated continuously to the anaerobic tank by a pump P. The nitrate nitrogen (NO 3 -N) concentration (mg / l) and COD (mg / l) of the treated water exiting the precipitation tank were measured. The result is shown in FIG.
As is clear from FIG. 3, nitrate nitrogen was almost completely treated from the first day of operation, and good treatment could be performed throughout the continuous treatment period as in Example 1. However, residual methanol-derived COD remains in the treated water, and it is necessary to install a re-aeration tank or the like to treat this.
[0017]
[Table 2]
【The invention's effect】
According to the present invention described above, nitrate nitrogen in waste water can be almost completely removed, and the residual BOD in waste water subjected to denitrification treatment is low in concentration, and aerobic treatment (re-aeration is performed with activated sludge). There is no need to install a tank) or to separate and return activated sludge.
Further, by installing the membrane separation device in the anaerobic tank, the separated sludge stays in the anaerobic tank, and no equipment for returning the sludge is required.
Therefore, by implementing the present invention, it is possible to efficiently and economically denitrify wastewater containing nitrate nitrogen in a narrow space.
[Brief description of the drawings]
1 is a schematic view of an apparatus used in Example 1. FIG.
2 is a schematic view of a conventional apparatus used in Comparative Example 1. FIG.
FIG. 3 is a diagram showing the processing results of Example 1 and Comparative Example 1;
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20682795A JP3819457B2 (en) | 1995-07-21 | 1995-07-21 | Biological denitrification of wastewater |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20682795A JP3819457B2 (en) | 1995-07-21 | 1995-07-21 | Biological denitrification of wastewater |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0929282A JPH0929282A (en) | 1997-02-04 |
| JP3819457B2 true JP3819457B2 (en) | 2006-09-06 |
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| JP20682795A Expired - Lifetime JP3819457B2 (en) | 1995-07-21 | 1995-07-21 | Biological denitrification of wastewater |
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| KR100336483B1 (en) * | 1999-02-27 | 2002-05-15 | 조양호 | Method for removing nitrogen from waste water through sulfur-utilizing denitrification |
| JP2002316189A (en) * | 2001-04-18 | 2002-10-29 | Hitachi Plant Eng & Constr Co Ltd | Biological treatment apparatus and autotrophic sulfur denitrification method |
| CN103803706B (en) * | 2014-03-04 | 2016-01-27 | 重庆耐德机械设备有限公司 | A kind of based on membrane bioreactor sewage water treatment method |
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